The central nervous system (CNS) consists of the brain and the spinal cord, as well as the retina.
The peripheral nervous system (PNS) extends outside the CNS. The PNS is divided into the somatic nervous system and the autonomic nervous system.
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. A typical neuron possesses a cell body (often called the soma), dendrites, and an axon.
A nerve is an enclosed, cable-like bundle of neural axons. Each nerve is a cordlike structure that contains many axons.
Each axon is surrounded by a layer of tissue called the endoneurium. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of tissue called the perineurium. The neuron or nerve is wrapped in a layer of tissue called the epineurium.